1. Field of the Invention
The present invention generally relates to a liquid-cooled, vertical shaft type combustion engine mounted on a working vehicle such as a lawn tractor and, more particularly, to an improvement in a duct system of the liquid-cooled, vertical shaft type combustion engine, in which a cooling fan is accommodated, for enhancing the cooling performance.
2. Description of the Prior Art
As is well known to those skilled in the art, some lawn tractors currently available in the market make use of a liquid-cooled, vertical shaft type combustion engine. The liquid-cooled, vertical shaft type combustion engine generally includes a radiator arranged within an engine compartment below a bonnet or hood at a front region of the lawn tractor and above the engine, a cooling fan positioned below the radiator, a duct accommodating the cooling fan therein and an air cleaner unit disposed above the duct. See, for example, U.S. Pat. Nos. 4,946,482 and 4,756,280 issued Aug. 7, 1990 and Jul. 12, 1988, respectively, to Tamba et al. and assigned Kawasaki Jukogyo Kabusghiki Kaisha.
In the prior art liquid-cooled, vertical shaft type combustion engine such as disclosed in those USPs referred to above, since the radiator is positioned immediately above a vertically extending crankshaft, the arrangement is made such that a downwardly oriented stream of cooling air drawn by the cooling fan to pass through the radiator from above is directed to flow through the duct and is, after having been acutely deflected by an air stream guide disposed inside the duct, discharged to the outside from front of the working vehicle. With this arrangement, however, a smooth flow of the cooling air cannot be obtained. In view of this, a duct system including the radiator, the cooling fan and the duct is required to be large to cool the engine sufficiently.
Further, the duct according to the above mentioned U.S. Pat. No. 4,946,482 is a resin molded article and is formed to cover not only an outer peripheral portion of the cooling fan but also an underside of the cooling fan and is therefore required to be bulky in size. In addition, in view of a limitation imposed on the die molding, the duct has to be of a split construction including upper and lower duct components, resulting not only in increase of the number of assembling steps, but also in increase of costs for preparation of the dies. Yet, considering that the air induced by the cooling fan is discharged directly outside the combustion engine from a front outlet of the duct, it cannot be said that maximized utilization of the cooling air is attained in terms of cooling of various component parts of the combustion engine.